Centrifuges having rotor rotating in a vacuum



3,347,453 CENTRIFUGES HAVING ROTOR ROTATING IN A VACUUM Filed May 13, 1963 K. GOERGEN Oct. 17, 1967 8 Sheets-Sheet 1 Fig.1

K. GOERGEN 3,347,453 CENTRIFUGES HAVING ROTOR ROTATING IN A VACUUM Oct. 17, 1967 8 Sheets-Sheet 2 Filed May 13, 1963 Oct. 17, 1967 K. GOERGEN 3,347,453

CENTRIFUGES HAVING ROTOR ROTATING IN A VACUUM Filed May 13 1965 8 Sheets-$heet 3 manual temperature control temperature metering 4. control device bridge servomotor sigi tch for moving Delay pus uttom rri r the Cover circuit *furopenmg amplifier battery the cover dew point, metering device with peltier element Fig. 2

K. GOERGEN 3,347,453 CENTRIFUGES HAVING ROTOR ROTATING IN A VACUUM Oct. 17, '1967 8 Sheets-Sheet 4 Filed May 13, 1963 CENTRIFUGES HAVING ROTOR ROTATING IN A VACUUM Filed May 13, 1963 8 Sheets-Sheet 5 V (bf/V70 A7094 400945 0a. 17, 1967 K. GQERGEN 3,347,453

CENTRIFUGES HAVING ROTOR ROTATING IN A VACUUM Filed May 13, 1963 8 Sheets-Sheet 6 Fig.4

K. GOERGEN 3,347,453 CENTRIFUGES HAVING ROTOR ROTATING IN A VACUUM Oct. 17, 1967 8 Sheets-Sheet 7 Filed May 13, 1963 23 Rm Km 3,347,453 CENTRIFUGES HAVING ROTOR ROTATING IN A VACUUM Filed May 13, 1963 K. GOERGEN Oct. 17, 1967 United States Patent Ofitice 3 347,453 CENTRIFUGES HAVIlIG ROTOR ROTATING IN A VACUUM The invention relates to centrifuges and in particular it is concerned with a centrifuge having a rotor which operates in a vacuum.

It is known that the rotors of high velocity centrifuges, i.e., centrifuges that operate at a velocity of more than 10,000 r.p.m. heat up considerably during operation owing to the friction of the surrounding air. The removal of the frictional heat presents a number of difiiculties which can only be overcome by technically elaborate measures but which are no longer applicable with centrifuges having velocities of more than 25,000 r.p.m., so that measures have been taken to operate the rotors at the said high velocities under a vacuum.

However, the gases that still remain in the vacuum cause a certain amount of frictional heat so that the rotor must be additionally cooled. This is obtained in a manner that, a temperature difference between the rotor chamber and the rotor is established by means of which the rotor temperature adjusts itself to a value resulting from its heat radiation and its heating caused by friction. With conventional cooling means, generally a cooling mantle in the rotor space and a cooling machine with direct injection or solo circulation cooling the rotor temperature can be regulated with an accuracy of approximately 105 C. Greater accuracy of the temperature that is adjusted at the rotor is, however, not attainable with the known devices, because owing to its heating capacity the cooling device follows temperature changes on the rotor with a delay in spite of control devices that are as accurate as possible.

Particularly for the determination of sedimentation constants by means of analytic centrifuges however, the maintaining of a relative and absolute accuracy of the rotor temperature of approximately C., i.e., approximately 50 times greater accuracy than what has been attained heretofore is desirable.

It is an object of the invention to provide a solution for the foregoing problem which not only leads to the intended success as far as the extremely accurate control of the rotor temperature is concerned, but beyond that affords further essential advantages with respect to heretofore conventional cooling means of the prior art. In accordance with the invention this problem is solved by the application of proportionately controlled thermo electric elements (Peltier elements) for regulating the temperature of a rotor of a high velocity centrifuge operated in a vacuum in which the control signal for the proportional control is derived from a thermistor bridge cir-' cuit which is used simultaneously for measuring the temperature of the rotor. In this manner there are obtained not only the known advantages of heat control devices operating in accordance with the Peltier effect as regards small space requirements, elimination of a cooling compressor and of the cooling agent leads, avoidance of any type of movable parts which are subject to wear, to interruptions or failure and which have to be tended but due to the small heat capacity of the device it is now possible to establish the desired temperature practically without inertia so that it is possible to do this more accurately as well as with simpler means than heretofore. This is due to the fact that the cooling action can be accurately measured by the control of the amper- Patented Oct. 17, 1967 age, can be suddenly eliminated and converted to a heating eifect by reversing the direction of the current. Since the cooling stops immediately as the current is disconnected, there results the additional advantage that on opening the rotor chamber after running of the centrifuge the cooling surfaces are not dampened and thus the apparatus is immediately ready for the next operation.

The dampening of heavily cooled surfaces in the rotor chamber with condensation from the ambient atmosphere leads to a reduction of the vacuum for the repeated operation of the centrifuge, because the large quantities of gas arising in accordance with the vapor pressure of the water can only be withdrawn by the vacuum pumps after a considerable length of time. That again results in that the centrifuge operates first not only with a relatively poor vacuum but also under variable vacuum conditions. The latter is particularly disadvantageous for centrifuge operation with rotors having pivotally mounted beakers or tumblers.

While the Peltier cooling undoubtedly provides only small output with a poorer degree of etficiency than the compressor cooling installations and causes higher production costs, their application however afifords extremely great advantages with centrifuges having rotors that operate in a vacuum which open up new possibilities of use for centrifuges of the type concerned, for example analytic operation with the Strohmaier cell which is particularly dependent on constant temperature.

The Peltier effect is obtained when a direct current passes through the contact between two conductors of different materials. An amount of heat is developed in the contact plane which is proportional to the current when the current flows in one direction. When the current is reversed this contact plane cools.

A Peltier element generally consists of two-semi-conductors of different materials which are connected, for example by means of a copper strip, and which at their other ends are each connected by a further copper strip with a current source. When a current flows heat develops where the current enters one of the two semi-conductor materials referred to as n-material, while the outgoing current end becomes cold. With the other semiconductor material generally referred to as p-material, heat is consumed and colddeveloped at the current entrance while the current exit end produces heat. Therefore the copper stripping or other material which connects the n and p-material becomes cold. The semi-conductor material used for the purpose may, for example, be telluric bismuth mounted between copper plates Semi-conductors show an essential advantage over ordinary materials which are subject to the Peltier eifect as they develop greater thermal forces.

Further details and advantages of the invention will become apparent from the following description with reference to the accompanying drawing in which:

FIG. 1 illustrates an embodiment of the centrifuge in accordance with the invention,

FIG. 1a is a view, partly in section, showing the centrifuge and the associated drive and control means,

FIG. 2 shows a schematic diagram of the embodiment described,

FIG. 2a is a view, drawn to an enlarged scale, showing the backs of two Peltier elements moved angularly into the plane of the drawing,

FIG. 3 is a detailed sectional view of the hollow rotor shaft and the associated vacuum sealed bearing, and the tempertaure measuring device,

FIG. 4 is a plan view of the dew point measuring device and of a Peltier element connected thereto,

FIG. 5 is a complete circuit diagram showing the circuits and connections for operating the Peltier elements,

temperature control measuring means and other associated components, and

FIG. a is a circuit diagram showing further features in detail.

A detailed description of Strohmaier cells of the type used in the apparatus in accordance with the invention can be found in [1.8. Patent No. 3,202,348 issued to K. Strohmaier.

A vacuum sealed chamber or housing 1 is provided with a nozzle 2 to which a vacuum pump (not shown) is connected. The chamber 1 is closed at the top by means of a cover 3 having a sealing ring 4 for the movement of which are provided rollers 5 running in a known manner during the opening and closing on rails 6, while a chain 8 is connected to the cover at 7, a reversing sprocket wheel 9 and the sprocket chain wheel 10 on the drive motor 11. A device provided on this cover operating mechanism that effects that the cover is somewhat raised during opening before movement to the side and on the other hand is lowered during closing of the brim of the chamber 3 is not shown for the sake of clarity. Likewise the end position switches which disconnect the drive motor in the end positions of the cover are not shown.

The drive assembly 12 for the centrifuge rotors has a drive shaft 13 and is brought into the chamber 1 in a vacuum sealed manner by way of a special stufiing box 14. The shaft 13 ends in a hollow shaft 15 upon which rotors 16 and 17 are secured by means of the nut 18. At the left and at the right different rotors are indicated. An angular rotor 16 in which the tumblers 19 are provided at a fixed angle with respect to the rotor axis, while the tumblers 20 of the rotor 17 are suspended vertically when the centrifuge is at rest and swing outwardly into the position indicated during running of the centrifuge. This type of rotor is required for the aforementioned Strohmaier cells.

In accordance with applicants earlier application, Ser. No. 253,790, a thermistor 21 is provided inside the shaft 15 for registering the temperature of the rotor, the indicated value of which is picked up by way of rotating coil 22 and fixed coil 23 at 24 without a contact being made. A mantle 25 of metal having good heat conducting quali-. ties is provided on the outside with series of Peltier elements 26 which are circumferentially distributed in a good heat conducting contact with the mantle. The series of elements 26 are provided on the back thereof with pockets 27 for a cooling liquid, preferably tap water, which is fed in at tubulation 28 and withdrawn at tubulation 29. The current supply for the Peltier elements is indicated at 30.

The bridge potential delivered by the temperature measuring device is compared in the control bridge in a differential circuit with a stabilized potential, the value or magnitude of which can be controlled. The value of this. comparing or standard potential is in a fixed relationship with the potential which is delivered by the temperature measuring means in proportion to the temperature thereof. If during the operation of the centrifuge a difference arises between the comparative or standard potential and the measured potential caused by temperature changes in the rotor, then this constitutes a measure for the deviation of the desired temperature value and the presently existing value.

The signal obtained is led to the reversing switch (push button for cover opening) which passes it on directly to the amplifier as the centrifuge is running. The amplifier delivers a current which is proportional to the signal to the Peltier elements which cool the rotor chamber and which in a given case heat the chamber after passing through the zero point of the bridge and reversal of the poles.

To the same extent as the Peltier elements of the rotor chamber are covered by condensation by the amplifier, energy is imparted to a single Peltier element in the dew point gauge. This Peltier element tempers a polished metal plate that is exposed to ambient air the reflection ability of which is registered in a known manner by the light source and a photocell. If the plate temperature falls below the dew point of the ambient air, then the plate is dampened so that the photocell emits a corresponding signal.

If upon termination of the running of the centrifuge the cover is to be opened by pressing the cover operating button, then the switch connection in the reversing switch from the control bridge to the amplifier is interrupted, the amplifier now receives the signal from the dew point gauge in a manner that the Peltier elements are switched to heating in the event that the temperature of the tempered reflection plate and thus also the temperature of the rotor chamber are below the dew point of the ambient By pressing the cover operating button a delaying member is simultaneously energized which after a fixed time period that is required as a maximum for heating the chamber releases the automatic opening of the chamber cover through the servomotor. In this manner the dampening of the cooling surfaces in the chamber is avoided.

In FIG. 1athe centrifuge in accordance with FIG. 1 is illustrated as it is installed on a frame in a housing, where the frame 201 is covered by plates 200 on the sides and on top by a cover plate 202 which has an aperture 203 which provides access to the vacuum chamber after the cover is removed from the chamber. The different switches, push buttons and indicating instruments are mounted on the switch panel 204.

Horizontal support members 131 which divide the housing into a lower and an upper portion provide support for the rotor drive means including the motor 12. This motor is connected with the transmission housing 207 by way of a flange 208, and the transmission housing is fastened to the left member 131 by way of resilient elements 205, only one of which is shown, with screws that extend through the transmission cover plate 206. A base plate 130 is mounted on top of the support members 131, which plate supports the rotor chamber.

A revolution indicator 210 is connected to the motor which has a pole wheel magnet, a stator plate and two coils. This indicator is utilized in adjusting the rotational speed of the motor and thereby of the rotor, which must be accurately controlled for centrifuging sensitive preparations. It is, of course, possible to provide other means for controlling the speed of the centrifuge.

A gear 211, preferably of plastic material, is mounted on the shaft of motor 12 and engages pinion 212 that is connected to the shaft 13 of the rotor. A bearing member 213 rotatably supports this shaft 13 at the lower end and the upper end extends through the sealing stuffing box 14 and through the means for measuring the temperature in the rotor described hereinabove and for which a connecting plug 214 is provided. Since the temperature would rise if the water cooling were interrupted, a water flow checking device 217 is provided, which, together with a magnet valve 218, serves for continuously even water flow from the water source 219 through the temperature measuring device. Oil is supplied to the stufiing box 14 at from a container 121 to provide for proper sealing of the rotor vacuum chamber at the shaft 13.

A vacuum container 123 serves for separating the stuffing box oil which is drawn into the vacuum chamber from the passage of the shaft 13. An oil release valve 129 is provided on the container 123 for removing the oil. The vacuum pump is indicated at 124 which is driven by a separate motor 126 by means of V-belts. The pump 124 and its motor 126 are mounted on a base plate 127 secured to the lower part of the housing by way of rubber and metal elements 128. i

The bottom of the rotor chamber is defined by a plate 31 of insulating material, and the chamber is surrounded by an outer mantle 32 which is sealed vacuum tight by means of O-rings 33 against base plate 130. The outer mantle 32 supports top member 34 of substantially annular configuration which may be welded to the mantle. Between part 34 and the casing plate 3 which closes the rotor chamber during operation, a further O-ring seal 4 is provided. Strong safety rails 38 are arranged above the cover 3 which is slidable after being raised to prevent the cover from being cast upwardly in the event of a rotor explosion.

An inner armor mantle 39 is arranged inside mantle 32 which extends from the plate 31 of insulating material to the top member 34. The double wall construction of the rotor chamber obtained in this manner provides for improved insulation.

Eight Peltier batteries 26 are mounted in plan milled areas 28 around the outer surface. The back ends 27 which are disposed outwardly present cooling pockets through which the cooling water flows. The specially milled surfaces at 41 provide for best possible heat transfer as heat is withdrawn from the inner rotor chamber 1. Band straps 44 support the Peltier batteries 26 on the outside of the wall 25. The cooling pockets 27 of the Peltier elements are connected with one another by tubular elements 45.

A rubber member 46 serves for elastic vacuum sealing between the rotor shaft 13 and the chamber, and a flange 47 retains the rubber element 46 in its position.

The construction and mounting of the Peltier batteries together with the water and current supply thereto is illustrated more in detail in FIG. 2a where two of the eight batteries that are provided are shown as seen from the outside and are, for the sake of clearer illustration, projected into the plane of the drawing. The cooling pocket 27, which is seen from the rear, is preferably made of brass. As seen in the section, the pocket forms a chamber, to the lower end of which a tubular element or pipe 45 is connected through which the cooling Water flows and from the upperend of which a pipe connection 45a extends to the lower end of the adjacent battery or cell. In this manner all cooling pockets 27 are connected in series with the circuit of cooling water. On the inside of the cooling pockets which faces the axis of the rotor, the actual Peltier elements are secured by means of screws 52.

The tubular elements or pipes 45 or 45a are preferably made of copper, while the supply and discharge tubes 28 and 29 are preferably made of plastic material such as polyamide. Threaded connecting elements 53 are used for joining the copper pipe sections 57 with the pipes 58. The portions of the copper tubes 57 that pass through the plate 31 which is of plastic material serve at the same time for supplying electric current to the Peltier elements. In this manner it is possible to avoid separate passages into the vacuum chamber. Cable clamps 59 are provided for electrical connections, which also serve to avoid sliding of the tube members 57 relative to the flange 62, and electrical leads 30 are connected to said clamps. Further cable clamps 56 are provided above the plate 31 and electric leads 55 and are connected to the Peltier batteries or elements that are arranged in series. For vacuum-tight sealing of the tubes or pipes 57, O-rings 61 are provided which are arrangedin recesses in the plate 31 and which are pressed by the mounting screws 63 against the pressure flange 62.

In FIG. 3 the temperature sensing means in the rotor shaft are illustrated drawn to a larger scale. The pinion.

212 on the rotor shaft 13 meshes with the toothed gear 211. The shaft 13 is journalled in bearing member 213 by means of a ball bearing 65 in the bushing 67. The upper ball bearing 64 is seated in an intermediate sleeve 66 which permits of mounting the pinion 212 from the top.

A pin of spring steel is received at its lower end in a groove in the pinion and is rotated therewith. A stuffing box 69 of bearing material is provided and an intermediate plate 70. A tube 71 is connected by means of a nipple to supply oil re the stuffing box, and the hollow screw 72 fixes the stufling box 69 in position and allows oil to flow to the pin 68, transverse bore 73 and thus to the stuffing box.

The cooling water supply tube 74 (which is shown displaced by 90) feeds in the water for cooling the bearing. A milled water channel in the form of a slot 76 is provided in the stufiing box 69. On the other side (not shown) a similar slot for discharging the cooling water leads to the outlet pipe (likewise not shown) for the cooling water. Thus the Water enters from the conduit 74 through bore 75 into channel 76 into the stufling box, thence rises and passes through a recess 77 to the opposite slot. The O-ring 78 provides for a tight seal between the water cooling system and the evacuated space above it, the O-ring 79 provides a tight seal between the water and the oil while the O-ring 80 is provided below for sealing the oil.

The vacuum suction connection is in communication with the connection 2. A coil support 82 carries the stationary coil which is a component of the means for transmitting measured temperature factor. A sleeve 84 serves to protect the coil 24 and engages with its outside the rubber member 46.

Further O-ring seals 85 and 86 are provided for sealing the coil space which is under normal pressure. Connecting leads 87 are brought out to the contact element 214 which is held in place by a plate 89.

A further vacuum seal O-ring 90 is provided between the coil support 82 and the intermediate plate 70. A screw 91 serves for fastening the sleeve 84 on the coil support 82. One of the three screws for fastening the assembly disposed around the shaft to the plate 70 is indicated at 92.

The pin 68 is rigidly secured by soldering or the like to the shaft 15 which carries the rotor. Furthermore a thermistor 94 is mounted in a fitting 95. The fitting serves as a support for the shaft 15 and for conducting the heat from the shaft to the thermistor. The connecting leads of the thermistor shown at 97 lead to a coil 22 which is preferably supported by a coil carrier 99 made of plastic material which is encased in a protective housing 100 of plastic material.

It is noted that the pivotable tumbler mounted on the rotor 17 is particularly suited for operations with Strohmaier cells. A Strohmaier cell is a container for determining the sedimentation constant of dispersed macromolecular substances, and it is in the form of a test tube, the interior of which narrows down toward the neck and a short distance therefrom While forming a shoulder below the neck opening. In the space between the inside of the tube and the outer surface thereof channels are formed of different height which extend laterally into the wall and up wardly to the top surface of the cell.

The device shown in FIG. 4 for measuring the dew point serves for preventing formation of humidity before the opening of the rotor chamber and after completion of a centrifuging operation. If the temperature of the rotor chamber should be too low prior to opening so that there is a danger of moisture depositing in the chamber, the chamber is sufficiently warmed by suitable reversal of the Peltier batteries.

The device for preventing or controlling the moisture deposit in the interior of the rotor consists of a housing of sheet steel 101 having air slots 102. The Peltier battery 103 is disposed in the housing, and it is provided with a cooling pocket 104 and coolant inlet and outlet conduits- An incandescent lamp 106 is mounted in the socket 107, The light ray of the lamp 106 is directed against the Peltier element 103 which has a reflecting surface, and the light is reflected against a photocell 111. The photocell is supported by an angular member 112 and the lamp 106 by an angular member 110. The electric wires of the lamp of the photocell and of the Peltier element are brought out to a terminal strip 113 at which other connections are also made. As soon as the reflecting plate on the Peltier element 103 becomes frosted so that less light is directed against the photocell 111, an electric impulse is emitted which switches the Peltier elements to the heating condition.

The control circuit for the Peltier element is illustrated in FIG. 5. A DC potential derived from a temperature measuring element is supplied to the terminals 45, 46 and thence by way of a resistor 314 to a vibrating contact 315. This vibrating contact is at the same time supplied with the stabilized DC potential by way of resistor 316, potentiometer 317, the contact of the potentiometer and to resistor 319. The coil of the vibrator is supplied with a pulsating direct current which is supplied by way of a terminal 321 that is produced by a diode 322. The direct that is converted to alternating current is supplied to the grid of the amplifier 323. The control grid of this tube is connected to ground by way of a grid resistor 324 while the cathode is also connected to ground through a parallel circuit comprising a cathode condenser 326 and cathode resistor 325. The anode of the tube 323 is connected by way of an anode resistor 327 to a terminal 447 which supplies a positive anode potential while the screen grid is directly connected with this terminal. In order to prevent over-modulation of the following amplifier stage a limiting stage is connected to tube 323 which provides for double limitation and which consists of a duodiode 328. The cathode of the first system of this tube is connected by way of a coupling condenser 320 and a coupling resistor 330 with the anode of the tube 323. The cathode of the tube system I is connected to the anode of the tube system II and by way of resistor 331 to the terminal 447. The correct operating condition of the duodiode is also determined by the resistor 332, the condenser 333 and the resistor 334, one end of which is connected to the anode of the tube system I and the other to ground (resistor 332, condenser 333), respectively, to the terminals 321 (resistor 334). The operating condition is furthermore determined by the resistor 337 which leads from ground to the cathode of the tube system II and by the resistor 335 which is connected with the same electrode and to the positive terminal 336. The potential limited by this stage is supplied by way of grid 339 of the following amplifier stage. The control grid of this tube is connected to ground by way of a grid leak resistor 340, while the cathode is also connected to ground by way of a parallel circuit comprising the cathode resistor 341 and the condenser 342. The anode of the tube 339 is connected to the terminal 347 by way of a resistor 343, while the screen grid is directly connected to this terminal. The initial signal derived from the anode of the tube 339 is supplied by way of a condenser 344 to the control grids of a double triode, which are connected with one another and which are also connected to ground by way of a grid leak 346. The cathodes of this tube which are likewise connected are connected to ground, on the one hand by way of a parallel circuit comprising a resistor 347 and a cathode condenser 348 and, on the other hand, by way of a variable resistor 349 to the terminal 347. By setting the resistor 349 the double triode may be adjusted in such a manner that when no current flows in the bridge, the two systems are closed.

The primary winding of a transformer 350 is connected at one end to the anode of the tube system I and at the other end to a terminal 352, while the primary winding of the second transformer 351 is connected at the one end to the tube system II and at the other end to a clamp 353. The two clamps 352 and 353 are supplied with an alternate potential of opposite phase from the line transformer. The double triode 345 is so adjusted by varying the resistance of the resistor 349 that at balance of the potentials supplied through terminals 45, 46, the two systems are closed. If the potential yielded by the temperature measuring device varies with respect to zero either toward the positive or the negative side, then the anode system of equal phase becomes conductive and a potential is induced in the secondary winding of the particular transformer 350 or 351. The secondary windings are connected with the grid of a double triode 354, the cathodes of which are connected together and grounded by way of a parallel circuit comprising a cathode resistor 355 and a cathode condenser 356. Each anode connected to one end of the primary winding of a transformer 357 or 358, while the other ends of these primary windings are connected together and to a terminal 359 which carries the positive DC potential. The potential induced in the secondary windings of the transformers 357 or 358 is rectified in a rectifier circuit comprising a diode 360 and a condenser 361 or a diode 362 and a condenser 363 and is supplied as a positive potential by way of a resistor 364 or 365 to the grid of a tube 366 or 367. The control grids of these tubes are also supplied by way of resistors 368 and 369 with a negative potential which is derived from the terminals a or f. An alternating potential of opposite phase is applied to the anodes or to the screen grid of these two tubes 366 or 367, which on the one hand is conducted by way of terminals 370 or 371 from the line and on the other hand by way of terminals 372 or 373, and is connected to the cathode resistors 374 or 375. The potential drop from the two cathode resistors 374 and 375 is picked up at the terminals b and e. The two tubes 366 and 367 are inoperative at zero potential.

The signal from the terminal b is supplied to the base of transistor 378 by way of a condenser 376. The base of this transistor is connected with the negative potential a by way of a resistor 380, while the collector is connected by way of a resistor 382 to the same potential. The emitter is connected to a terminal c. The measurement of the resistors connected with the transistor 378 is made in a manner that the transistor operates under A operating conditions. The output signal from the collector of this transistor is coupled to the base of a subsequent transistor 386 by way of a condenser 384 with the transistor 386 operating as an output transistor. The base of this transistor is connected to the terminal c while the emitter is connected directly. The stage containing the transistor 379 operating under A operating conditions and the transistor 387 operating as an output transistor is constructed in a similar manner, with the terminals a, b, 0 corresponding to terminals f, e, d and resistors 380, 382, 388 corresponding to resistors 381, 383, 389 and condensers 376, 384 to condensers 377, 385.

The primary windings of two three-phase transformers 417 and 418 are connected with the three-phase line by way ofterminals 402, 431, 432. The first ends of the three separate secondary windings of the transformer 417 are each connected to the positive connection of three rectifiers 419, 420, 421, the negative terminals of which are connected together and to the emitter of transistor 387. The second ends of these secondary windings are connected to the negative end of three further rectifiers 420, 423, 424, whose positive ends are connected together and with the emitter of transistor 386.

In a similar manner the first ends of the three separate secondary windings of the second transformer 418 are each linked to positive connections of three rectifiers 428, 429, 430, the negative terminals of which are brought together and connected to the transistor 386. The second ends of these secondary windings are each connected to the negative terminals of three further rectifiers 425, 426, 427, the positive ends of which again are brought together and connected to the emitter of the transistor 387. The Peltier battery 26 is connected in series aiding with the individual Peltier element 103. This series circuitv is connected at one end to the negative sides of the rectifiers 419, 420, 421 and at the other end to the negative sides of the connected rectifiers 428, 429, 430.

The circuit contains a transformer 390, the primary winding of which is connected to ground at one end and at the other end to the line by way of terminal 402. A secondary winding 391 at one end is connected to ground and at the other end to terminal 392. Two further series connected secondary windings 393, 394 are grounded at their common connection while the free ends are led to terminals 352, 353. A secondary winding 398 is grounded at one end and connected to a terminal 321 by way of a of the double triode 354 is rectifier 322. The first end of a secondary winding 399 is connected with terminal 370 While the other end is connected to terminal 371. The ends of a further secondary winding are connected to the terminals 371, 372, respectively. One end of the secondary winding 410 is grounded, while the other end is connected with the terminal 402. The AC input terminals of a rectifier bridge circuit comprising four rectifiers 403 are connected with the terminals of a secondary winding 395. The negative output terminal of the rectifier bridge is grounded, while the positive output connection is brought to the input terminal 396 of a stabilizing end filter stage.

Loading capacitor 404 leads from the terminal 396 to ground. A series circuit of resistors 408, 411 is provided between the terminals 396 and 359, while a potential stabilizing tube 405 is connected between the common terminal of resistors 411 and 408 and ground, and a filter condenser 414 is connected between the terminal 359 and ground. In a similar manner the terminal 396 is connected by way of series connected resistors 409, 412 to the terminal 336, while between the common connection of these resistors and ground a potential stabilizing tube 407 is provided and between terminal 336 and ground a filtering capacitor 416. Futhermore, a series circuit leads from the terminal 396 to terminal 447, which circuit includes resistors 410 and 413, while a potential stabilizer tube 406 is connected between the commonconnection of these resistors and ground and a filter resistor 415 is provided between the terminal 447 and ground.

The circuit for the power operated cover and the dew point control extends from the terminal 402. of the line portion by way of a limiting contact 446, a terminal 397', a relay coil 434, a terminal 397 and a push button 433 to ground. Between the terminal 397 and terminal 397 the excitor coil of the timing device 435 is inserted while the drive motor 11 for the cover movement is connected to the terminals 397 and 397 with contact 444 of the timing device 435 therebetween. Furthermore a branch circuit is provided between terminal 397 by way of switch contact 436 of relay 434 to ground. When the push button switch 433 is operated, the relay 434 operates and closes its contact 436, thus operating the dew point control to be described below and the timing device. This operating condition is maintained also after opening of the push button switch because relay 434 is self-retaining. After the expiration of the time for which the timing device 435 is set, the contact 444 is closed and the motor runs until its circuit is opened by the limiting contact 446 in the opened condition of the cover.

Between the terminal 321 of the line portion and the terminal 397 an incandescent lamp 106 is connected at one end and at the other end a series circuit comprising a base resistor 438 and a photocell 111. The lamp 106 operates the photocell in a manner described in connection with FIG. 4. Since the Peltier element 103 is supplied with the same current as Peltier battery 26, the battery will be at the same temperature. The reflective capacity of the polished surface on element 103 changes when this surface is coated or frosted. Depending on the condition of the surface of the Peltier element 103, the light ray supplied to the photocell changes so that its internal resistance varies correspondingly. As a result a resistor 437 is closed or opened, the base of which is connected to the common terminal of photocell 111 and base resistor 438. The emitter of this transistor is connected by way of an emitter resistor 442 to the terminal 397, while the collector of this transistor is connected by way of a transistor 440 to the terminal 321. In order to effect reliable operation of the relay 443, a further amplifier stage is connected which contains resistor 439. The base of this resistor is connected to the emitter of transistor 437 while the emitter is connected by way of resistor 441 to the emitter of transistor 437. The relay coil 443 is connected as a collector resistor between terminal 321 and the collector of transistor 439.

With the polished surface coated or frosted the contact 318 of relay 443 reverses, so that the amplifier is furnished an impulse to heat. As soon as the polished surface is freed of the precipitation, the relay 443 withdraws its contact 318. If subsequently the timing device 435 closes its contact 444 and the cover motor 11 has opened the cover, the timing device 435, relay 434 and the dew point measuring device become inoperative simultaneously with the opening of the motor circuit.

I claim:

1. In a centrifuge having a vacuum sealed housing having an air tight and movable cover, a rotor mounted for rotation in said housing, a heat conducting element disposed around said rotor and supporting as sole cooling and heating source a plurality of Peltier elements, measuring means connected to said rotor for measuring the rotor temperature, conducting means connected to said Peltier elements and in receiving relationship to said measuring means for controlling the operation of said Peltier elements, said Peltier elements being adapted to cool the interior of said housing during centrifuging and to heat the interior of said housing prior to the opening of said cover, thereby avoiding condensation and development of moisture when said cover is opened.

2. In a centrifuge having a vacuum sealed housing having an air tight and movable cover, a rotor mounted for rotation in said housing, a heat conducting element disposed around said rotor and supporting as sole cooling and heating source a plurality of Peltier elements, measuring means connected to said rotor for measuring the rotor temperature, conducting means connected to said Peltier elements and in receiving relationship to said measuring means for controlling the operation of said Peltier elements, said Peltier elements being adapted to cool the interior of said housing during centrifuging and to heat the interior of said housing prior to the opening of said cover, thereby avoiding condensation and development of moisture when said cover is opened, said measuring means including a thermistor circuit in the shaft of said rotor, a coil to which said thermistor is connected and an amplifier in the circuit between said measuring means and said Peltier elements.

3. In a centrifuge having a vacuum sealed housing having an air tight and movable cover, a rotor mounted for rotation in said housing, a heat conducting element disposed around said rotor and supporting as sole cooling and heating source a plurality of Peltier elements, measuring means connected to said rotor for measuring the rotor temperature, conducting means connected to said Peltier elements and in receiving relationship to said measuring means for controlling the operation of said Peltier elements, said Peltier elements being adapted to cool the interior of said housing during centrifuging and to heat the interior of said housing prior to the opening of said cover, thereby avoiding condensation and development of moisture when said cover is opened, said measuring means including a thermistor circuit in the shaft of said rotor, a coil to which said thermistor is connected, an amplifier in the circuit between said measuring means and said Peltier elements, and a control bridge connected intermediate said measuring means and said amplifier.

References Cited UNITED STATES PATENTS 2,885,188 5/1959 Pickels et a1. 23326 3,019,609 2/1962 Pietsch 623 3,096,624 7/1963 Charos 623 3,129,174 4/1964 Pickels et al. 233-11 3,174,291 3/1965 Crawford et al 62-3 3,202,348 8/1965 Strohmaier 233-26 M. CARY NELSON, Primary Examiner.

HENRY T. KLINKSIEK, Examiner. 

1. IN A CENTRIFUGE HAVING A VACUUM SEALED HOUSING HAVING AN AIR TIGHT AND MOVABLE COVER, A ROTOR MOUNTED FOR ROTATION IN SAID HOUSING, A HEAT CONDUCTING ELEMENT DISPOSED AROUND SAID ROTOR AND SUPPORTING AS SOLE COOLING AND HEATING SOURCE A PLURALITY OF PELTIER ELEMENTS, MEASURING MEANS CONNECTED TO SAID ROTOR FOR MEASURING THE ROTOR TEMPERATURE, CONDUCTING MEANS CONNECTED TO SAID PELTIER ELEMENTS AND IN RECEIVING RELATIONSHIP TO SAID MEASURING MEANS FOR CONTROLLING THE OPERATION OF SAID PELTIER ELEMENTS, SAID PELTIER ELEMENTS BEING ADAPTED TO COOL THE INTERIOR OF SAID HOUSING DURING CENTRIFUGING AND TO HEAT THE 